It's not always need a big fish tank. When I was a small boy, I nagged my parents that I would get an aquarium. Dad had one and knew how much work it could demand and was afraid that I would not manage it. He gave me a glass jar and 7 liters (1.5 gallons) of water. I had this for a year and learned a lot of the basics with the help of some swordtail and guppies. Then I got the confidence of more demanding fish and larger fish tanks.